Information technology is becoming more and more present in building information applications. Examples and applications include energy saving which may be accomplished by combining and processing information available from a information technology network of the building. By using these information technology networks also control of illumination of the building may be more and more integrated. To limit the installation effort and cost in a building, it could be advantageous to use one electric cable for several purposes. Such an electrical cable could be used for both provision of power and communications. One such example is power-line communications. Another example is to use the IEEE standard Power over Ethernet (PoE) defined according to IEEE 802.3af. This standard defines the interaction between power sourcing equipment (PSE) and power devices (PD). One Ethernet cable can transport both data and power (e.g. 13 W) to the PD. Making use of efficient solid state lighting (SSL) sources, such as light emitting diodes (LEDs), the power delivered by one Ethernet cable will be sufficient (with the LEDs approaching 200 Im/W) to illuminate e.g. a work desk or another limited office space, such as an area next to a printer. On the market, there are certain PD controllers available, typically as integrated circuits. These PD controllers are attached as an interface between the lighting device to be controlled and the Ethernet cable. One example of such an integrated circuit is the LM5073 circuit from National Semiconductor. A drawback is that the PD controller adds cost, volume and losses to the circuitry of the lighting device to be controlled.
As noted above, PD controllers can be used in lighting contexts. Particularly, PD controller may be used to control lighting devices. PD controllers according to prior art have the possibility to shut down the lighting device by two means. Firstly, according to the PoE standard there is a shut down signal commanding the lighting device not to conduct any current. Secondly, the PD controller can cut the power flow to the lighting device by means of an internal switch. In both cases, any activity of the controller will lead to undesired effects on the light output.